The present invention relates to AC and DC motors and, more particularly, to flux rings for the motors.
In order to improve motor performance, Rare Earth magnet such as Injection Bonded Neodymium-Iron-Boron (N.I.B.) magnet is used. However, the rated operating temperature of the Injection Bonded N.I.B. magnet is typically in the range of 120° C. Thus, the power tool can be operated only up to this limited temperature. Also, the Injection Bonded N.I.B. magnet, particularly the isotropic N.I.B. magnet, is very hard to magnetize radially. The material costs increase dramatically when anisotropic material which enables radial magnetic field orientation is used.
The present invention provides the art with motor magnets which provide increased thermal performance. The magnets are also easier to magnetize such that the radial components of the magnets are directed to the center of the flux ring. Also, the magnets are cost-effective.
According to a first aspect of the invention, a flux ring for a motor comprises a ring which fits inside a motor can of the motor. At least one magnet is positioned on the ring. The at least one magnet includes a portion formed from an isotropic magnetic material and a portion formed from an anisotropic magnetic material. Generally, both magnets are formed from the isotropic and anisotropic materials. The isotropic as well as anisotropic materials are magnetic powders. Also, the isotropic and anisotropic magnetic materials are in a resin which enables the material to be injection molded onto the ring. The isotropic magnetic material portion is sandwiched between two anisotropic magnetic material portions such that the isotropic magnetic material portion is on an arc circle of between 40° and 50°. The magnet itself is on an arc circle of about 140° about the ring. The isotropic magnetic material portion is generally located on the poles of the motor.
In accordance with a second aspect of the invention, a method of manufacturing a flux ring comprises providing a ring having an anchoring mechanism. Placing the ring in a die. Molding a first isotropic magnetic material onto the ring where the anchoring mechanism secures the first isotropic magnetic material to the ring. Molding a second anisotropic magnetic material onto the ring adjacent the first isotropic magnetic material. The anchoring mechanism secures the second anisotropic magnetic material to the ring. Further, the anisotropic magnetic material is molded on two sides of the first isotropic magnetic material. The first isotropic magnetic material is molded without a magnetic field present. The second anisotropic magnetic material is molded under a magnetic field of about 1400–1600 amp/meter. Also, the first isotropic magnetic material is molded along an arc circle of the ring along 40° to 50° of the circle. The second anisotropic magnetic material is molded along the circle such that the magnet covers about 140° of the circle.
In accordance with a third aspect of the invention, a motor comprises a stator assembly with the stator assembly including a flux ring. The flux ring comprises an annular housing. At least one molded magnet is received on the housing. An anchor mechanism on the housing retains the at least one magnet on the annular housing. At least one magnet is positioned on the ring. The at least one magnet includes a portion formed from an isotropic magnetic material and a portion formed from an anisotropic magnetic material. Generally, both magnets are formed from the isotropic and anisotropic materials. The isotropic as well as anisotropic materials are magnetic powders. Also, the isotropic and anisotropic magnetic materials are in a resin which enables the material to be injection molded onto the ring. The isotropic magnetic material portion is sandwiched between two anisotropic magnetic material portions such that the isotropic magnetic material portion is on an arc circle of between 40° and 50°. The magnet itself is on an arc circle of about 140° about the ring. The isotropic magnetic material portion is generally located on the poles of the motor. Also, the motor comprises an armature rotatable within the stator assembly. A commutator is rotatable with the armature and connected to the armature via a shaft. A brush assembly is associated with the commutator.
In accordance with a fourth aspect of the invention, a power tool comprises a housing with a motor in the housing. The motor comprises a stator assembly with the stator assembly including a flux ring. The flux ring comprises an annular housing. At least one molded magnet is received on the housing. An anchor on the housing retains the at least one magnet on the annular housing. At least one magnet is positioned on the ring. The at least one magnet includes a portion formed from an isotropic magnetic material and a portion formed from an anisotropic magnetic material. Generally, both magnets are formed from the isotropic and anisotropic materials. The isotropic as well as anisotropic materials are magnetic powders. Also, the isotropic and anisotropic magnetic materials are in a resin which enables the material to be injection molded onto the ring. The isotropic magnetic material portion is sandwiched between two anisotropic magnetic material portions such that the isotropic magnetic material portion is on an arc circle of between 40° and 50°. The magnet itself is on an arc circle of about 140° about the ring. The isotropic magnetic material portion is generally located on the poles of the motor. Also, the motor comprises an armature rotatable within the stator assembly. A commutator is rotatable with the armature and connected to the armature via a shaft. A brush assembly is associated with the commutator. Also, the power tool includes an output member coupled with the motor shaft. An actuator member is electrically coupled between the motor and the power source to energize and de-energize the motor. In turn, when the motor is energized, the output member rotates.
Additional objects and advantages of the present invention will become apparent from the detailed description of the preferred embodiment, and the appended claims and accompanying drawings, or may be learned by practice of the invention.